In recent years, with an increase in the degree of integration and capacity of a large scale integrated circuit (LSI), a circuit line width required for semiconductor devices has been reduced. In a case where a semiconductor device is manufactured, a pattern of, for example, wiring lines or holes formed in a photomask (also referred to as a reticle) is transferred onto a wafer by a reduced size projection exposure apparatus. The pattern formed on the photomask is reduced and projected to form a fine pattern on the wafer.
It is necessary to reduce the number of defects on the wafer in order to achieve high production yield of semiconductor devices. Examples of the defect on the wafer include abnormality in the shape of the pattern, abnormality in the dimensions of the pattern, and foreign materials on the pattern. As the size of the pattern becomes smaller, the size of defects affecting production yield also becomes smaller. Therefore, a pattern inspection apparatus for inspecting patterns requires high defect detection capability.
In an optical pattern inspection apparatus, the wavelength of inspection light is reduced in order to improve the defect detection capability of the pattern inspection apparatus. For example, a far ultraviolet laser is used as a light source of the inspection light. The resolution of an acquired inspection image is improved by reducing the wavelength of the inspection light.
In addition, an electron-beam-type pattern inspection apparatus has also been achieved in order to improve the defect detection capability of the pattern inspection apparatus. The electron-beam-type pattern inspection apparatus emits electron beams onto a wafer, detects secondary electrons emitted from a pattern on the wafer or electrons reflected from the wafer, and acquires an inspection image. There is an electron-beam-type pattern inspection apparatus that irradiates a wafer with multiple beams including a plurality of electron beams and acquires an inspection image in order to improve inspection throughput.
In the electron-beam-type pattern inspection apparatus, there is a concern that an inspection image will be changed by the influence of the electrification of a pattern in a portion which is repeatedly irradiated with electron beams. There is a concern that the defect detection capability of the pattern inspection apparatus will be reduced due to the change in the inspection image caused by the influence of the electrification of the pattern.